\begin{tikzpicture}

\definecolor{darkgray176}{RGB}{176,176,176}
\definecolor{darkorange25512714}{RGB}{255,127,14}
\definecolor{steelblue31119180}{RGB}{31,119,180}

\begin{groupplot}[group style={group size=2 by 2}]
\nextgroupplot[
tick align=outside,
tick pos=left,
title={not equal, looks like ellipse},
x grid style={darkgray176},
xmin=-3.1100318, xmax=3.2909539,
xtick style={color=black},
y grid style={darkgray176},
ymin=-3.2498656, ymax=3.2498656,
ytick style={color=black}
]
\addplot [semithick, steelblue31119180]
table {%
3 0
2.2981333 1.9283628
0.52094453 2.9544233
-1.5 2.5980762
-2.8190779 1.0260604
-2.8190779 -1.0260604
-1.5 -2.5980762
0.52094453 -2.9544233
2.2981333 -1.9283628
3 -7.3478808e-16
};

\nextgroupplot[
tick align=outside,
tick pos=left,
title={equal, looks like circle},
x grid style={darkgray176},
xmin=-3.1100318, xmax=3.2909539,
xtick style={color=black},
y grid style={darkgray176},
ymin=-3.2498656, ymax=3.2498656,
ytick style={color=black}
]
\addplot [semithick, steelblue31119180]
table {%
3 0
2.2981333 1.9283628
0.52094453 2.9544233
-1.5 2.5980762
-2.8190779 1.0260604
-2.8190779 -1.0260604
-1.5 -2.5980762
0.52094453 -2.9544233
2.2981333 -1.9283628
3 -7.3478808e-16
};

\nextgroupplot[
tick align=outside,
tick pos=left,
title={looks like circle, even after changing limits},
x grid style={darkgray176},
xmin=-3, xmax=3,
xtick style={color=black},
y grid style={darkgray176},
ymin=-3, ymax=3,
ytick style={color=black}
]
\addplot [semithick, steelblue31119180]
table {%
3 0
2.2981333 1.9283628
0.52094453 2.9544233
-1.5 2.5980762
-2.8190779 1.0260604
-2.8190779 -1.0260604
-1.5 -2.5980762
0.52094453 -2.9544233
2.2981333 -1.9283628
3 -7.3478808e-16
};

\nextgroupplot[
tick align=outside,
tick pos=left,
title={still equal after adding line},
x grid style={darkgray176},
xmin=-3, xmax=3,
xtick style={color=black},
y grid style={darkgray176},
ymin=-3, ymax=3,
ytick style={color=black}
]
\addplot [semithick, steelblue31119180]
table {%
3 0
2.2981333 1.9283628
0.52094453 2.9544233
-1.5 2.5980762
-2.8190779 1.0260604
-2.8190779 -1.0260604
-1.5 -2.5980762
0.52094453 -2.9544233
2.2981333 -1.9283628
3 -7.3478808e-16
};
\addplot [semithick, darkorange25512714]
table {%
0 0
4 4
};
\end{groupplot}

\end{tikzpicture}
